Strontium sealed source

ABSTRACT

The disclosure pertains to a strontium-90 sealed radiological or radioactive source, such as may be used with treatment of the eye or other medical or industrial processes. The sealed radiological source includes a toroidal shaped strontium radiological insert within an encapsulation. The encapsulation includes increased shielding in the center thereof.

This application is a continuation application of U.S. patentapplication Ser. No. 16/400,194, filed on May 1, 2019, now U.S. Pat. No.10,950,362, which is a continuation of U.S. patent application Ser. No.15/571,310, filed on Nov. 2, 2017, now U.S. Pat. No. 10,714,226, whichclaims priority of PCT/US2016/022437, filed Mar. 15, 2016, which claimspriority under 35 U.S.C. 119(e) of U.S. provisional application Ser. No.62/158,091, filed on May 7, 2015, the contents of which is herebyincorporated by reference in its entirety and for all purposes.

BACKGROUND OF THE DISCLOSURE Field of the Disclosure

The disclosure pertains to a strontium-90 sealed source, such as may beused with treatment of the eye or other medical, brachytherapeutic orindustrial processes. In particular, a relatively constant absorbed doserate is sought throughout a target volume of tissue of therapeuticinterest that is to be treated with radiation (hereinafter referred toas “a flat radiation profile”).

Description of the Prior Art

The prior art of radiological or radioactive sources of various typesfor medical, industrial and other processes is well-developed. Forexample, U.S. Pat. No. 8,430,804, entitled “Methods and Devices forMinimally-Invasive Extraocular Delivery of Radiation to the PosteriorPortion of the Eye”, issued on Apr. 30, 2013 to Brigatti et al., andassigned on its face to Salutaris Medical Devices, Inc., discloses anapplicator for minimally-invasive delivery of beta radiation from aradionuclide brachytherapy source to the posterior portion of the eye.In particular, this is adapted for the treatment of various diseases ofthe eye, such as, but not limited to, wet age-related maculardegeneration. Other prior art includes U.S. Pat. No. 7,070,554 entitled“Brachytherapy Devices and Methods of Using Them”, issued on Jul. 4,2006 to White et al., and assigned on its face to TheragenicsCorporation and U.S. Pat. No. 6,443,881, entitled “OphthalmicBrachytherapy Device”, issued on Sep. 3, 2002 to Finger.

While this prior art is well-developed and suited for its intendedpurposes, further improvements are sought in the radioactive sourcesused in the disclosed devices. In particular, a collimated distributionof radiation, rather than an isotropic (spherical “47π”) distribution ofradiation, would allow a radiological source to direct radiation at thetissues under treatment, while reducing radiation directed atsurrounding tissues which are not under treatment.

OBJECTS AND SUMMARY OF THE DISCLOSURE

It is therefore an object of the present disclosure to provideimprovements in the radiological sources used in brachytherapy and inother medical or industrial applications. In particular, it is an objectof the present disclosure to provide improved radiological sources forknown applicators for treatment of diseases of the eye, including, butnot limited to, wet age-related macular degeneration. These radiologicalsources are intended to concentrate the radiation on the diseasedtissue, rather than using isotropic radiation which would expose more ofthe surrounding healthy tissue to unnecessary radiation.

This and other objects are attained by providing a beta radiologicalsource, typically containing strontium-90, wherein the radiologicalinsert has increased radioactivity around its periphery and lessradioactivity at its center. This may be achieved by a toroidal orannular shape, (such as a donut-type shape with a hole or aperture inthe middle) or with the central portion of a disk having reducedthickness or reduced radioactivity content. This is further achieved byproviding an encapsulation with increased shielding in the center of theface from which the therapeutic radiation is emitted, therebysubstantially attenuating the radiation emitted from the central portionof a source. A further alternative uses a beta radiation collimatorgrid.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects and advantages of the disclosure will become apparentfrom the following description and from the accompanying drawings,wherein:

FIG. 1A is a top view of an embodiment of the radiological source of thepresent disclosure.

FIG. 1B is a perspective, cut-away view of an embodiment of theradiological source of the present disclosure.

FIG. 1C is a cross-sectional view along plane 1C-1C of FIG. 1A.

FIG. 2A is a plan view of the beta radiation collimator grid of thepresent disclosure.

FIG. 2B illustrates the operation of the beta radiation collimator gridcollimator grid in greater detail.

FIG. 3 is a cross-sectional view of a further embodiment of aradiological source of the present disclosure.

FIG. 4 is an illustration relating to the radiation dose profilegenerated by the radiological source of FIG. 3 .

FIGS. 5A-5F illustrates various further embodiments of the radiologicalsource of the present disclosure.

FIG. 6 illustrates a placement of the radiological source with respectto a human eyeball during medical treatment.

FIG. 7 illustrates a portion of FIG. 6 in greater detail.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings in detail wherein like numerals refer tolike elements throughout the several views, one sees that FIGS. 1A, 1Band 1C illustrate an embodiment of the radiological (or radioactive)source 100 of the present disclosure. Radiological source 100 includesan outer source encapsulation 102, typically made from a titanium alloy,stainless steel or similar material with suitable beta absorption andtransmission characteristics. Outer source encapsulation 102 includesouter cylindrical walls 104, an open circular top 106 and a circularfloor 108 forming a closed bottom. A circular cap 110, similarlytypically made from a titanium alloy, stainless steel or similarmaterial, is placed over the open circular top 106 and welded in placeafter all assembly has been completed, thereby resulting in a lowcylindrical configuration. A cylindrical inner source encapsulation-nest114, similarly typically made from a titanium alloy, stainless steel orsimilar material includes inner cylindrical walls 116, a closed circulartop 118 and an open circular bottom 120. The interior of innercylindrical walls 116 creates a generally cylindrical volume or cavity128 (see FIG. 1B, showing the cavity without a strontium-90 insert)which holds strontium-90 insert 130 (beta radiation source, see FIG.1C), which is typically in an insoluble refractory material such as aceramic or glass or a refractory-metal composite form such as aStrontium-90 compound mixed with a low density metal such as berylliumor aluminum. A beta emission collimator grid 140, typically of ahoneycomb configuration, is positioned immediately above, andcontacting, the circular floor 108 or closed bottom of outer sourceencapsulation 102 and immediately below, and contacting, thestrontium-90 insert 130 and the lower edge of inner cylindrical walls116 of inner source encapsulation 114. The resulting radiological source100 has a distribution of beta radiation 1000 (see FIG. 1C) which is notisotropic but which is substantially collimated (in part, by thefunction of collimator grid 140) so as to direct a greater portion ofthe beta radiation 1000 straight downwardly, in the illustratedorientation of FIG. 1C. The resulting radiological source 100 isintended to be particularly well-adapted for use with the medicalinstrument of U.S. Pat. No. 8,430,804, with the distribution ofradiation intended to allow the medical professional to direct theradiation to the treatment volume of the patient while minimizing theamount of unnecessary radiation directed to the surrounding healthytissues. See, for example, FIGS. 6 and 7 which illustrate a medicalinstrument 200 positioning the radiological source 100 behind a humaneyeball 2000 and directing radiation horizontally into the human eyeball2000.

It is noted that the strontium-90 beta radiation insert 130 may be madeof various materials, such as a strontium ceramic, strontium glass, or acollection of tightly packed ceramic beads (of various possible shapes)or a refractory-metal composite. Refractory ceramics and glassescontaining Strontium-90 can be made from a wide variety of materials incombination, such as those containing metal oxides of aluminum, silicon,zirconium, titanium, magnesium, calcium amongst others. It is envisionedthat other additional materials may be selected from, but not limitedto, such strontium-90 compounds as SrF₂, Sr₂P₂O₇, SrTiO₃, SrO, Sr₂TiO₄,SrZrO₃, SrCO₃, Sr(NbO₃)², SrSiO₃, 3SrO.Al₂O₃, SrSO₄, SrB₆, SrS, SrBr₂,SrC₂, SrCl₂, SrI₂ and SrWO₄. Additional, beta emitters based onmaterials other than strontium-90 may also be compatible with thisdisclosure.

FIGS. 2A and 2B disclose the beta collimator grid 140 in further detail.The object of the beta collimator grid 140 is to block or absorb asignificant portion of the non-orthogonal beta emissions while blockingor absorbing very little of the direct or orthogonal beta emissions fromthe strontium-90. The beta collimator grid 140 has a plurality ofhoneycomb-shaped open cells 142 (not drawn to scale) separated by walls144 (see FIG. 2B for walls 144). The non-orthogonal beta emissionsstrike the walls 144 of the honeycomb-shaped cells 142 and aresubstantially absorbed, while the direct or orthogonal beta emissionspass through the openings or passageways of open cells 142 withoutstriking the walls 144. In a typical example illustrated in FIGS. 2A and2B, the total thickness is 250 microns, the bar thickness is 30 microns,with a cell pitch of 260 microns and an aperture diameter of 230microns, resulting in an expected direct ray transmission of 78%. Thatis, 22% of the direct ray beta emission is attenuated. Those skilled inthe art, after review of this disclosure, will recognize that differentdimensions and numerical values may be used for similar applications. Itis envisioned that some embodiments may include the honeycomb-shapedcells 142 around the outer circumference of the collimator grid 140,with essentially 100 percent transmission near the center of thecollimator grid 140. This would increase the direct ray emission andnon-orthogonal emissions would likely impart their energy in atherapeutic region which the direct rays are also targeting. The otheradvantage of using a collimator grid in combination with a disk-shapedsource is a flat dose profile (i.e. a profile achieving a constantabsorbed dose rate throughout a target volume of tissue of therapeuticinterest that is to be treated with radiation). The effect of this isthat tissue at a certain depth and with a certain volume will receivethe same dose rate and uniform therapeutic dose without under orover-exposure of different parts of the therapeutic volume of interest.While a honeycombed hexagonal configuration is illustrated, thecollimator grid 140 could be square mesh or any other tightly nestingmesh geometry. The collimator grid 140 can be selected from variousmetals or non-metals which would absorb beta emissions, but which wouldsurvive normal operating conditions and potential accident hazardconditions such as an 800° C. fire, while not adversely interacting withother source components. Typical preferred materials include ironalloys, nickel alloys, molybdenum alloys, copper alloys, gold alloys,carbon and silicon. Those skilled in the art, after review of thepresent disclosure, will recognize that additional materials may be usedfor various applications. Additionally, the collimator grid 140 may beetched into the circular floor 109 of radiological source 100.

Collimation is more effective with photons than with beta particlesbecause photons scatter less in surrounding absorbers than betaparticles do. Photons are less easily attenuated (scattering less), betaparticles are highly attenuated (scattering more, as beta particles havethe same mass and charge as electrons so their collisions impart moreenergy per collision). Beta particles are also typically emitted with aspectrum of energies from zero to the maximum (2.28 meV in the case ofY-90, a decay product of Strontium-90), so their attenuation and scattercharacteristics differ greatly to mono-energetic photons, which areattenuated only by electromagnetic field interactions.

In order to produce a flat dose profile at the correct tissue depth infront of the presently disclosed beta source, the source outputtypically needs to accentuate the difference in dose rate at the centerversus dose rate in the periphery at the source surface. In other words,if the dose profile were to be flat at the source surface, it would notthen also be flat at a distance away from the source surface due toeffects of beta scattering in tissue. Therefore, it is typically desiredto produce an annular dose profile at the source surface which is muchlower in the center than in the periphery, so that it will become flatat the desired depth in tissue due to beta scattering in the tissue. Atfurther distances from the source, the tissue dose profile would becomeprogressively more spherical as more scatter and attenuation occurs.

The absorbing tissue effectively acts as a source of scatteredlower-energy radiation, which makes the dose profile less collimated andmore spherical at distances further removed from the source.

FIG. 3 illustrates a cross-sectional view of a further embodiment of theradiological source 100. The radiological source 100 is substantiallyrotationally symmetric, including cylindrical, annular and toroidalshapes. A capsule body 300, typically made of titanium or stainlesssteel, includes a lower floor 302 with a central plateau 304 therebyforming a toroidal channel 306 between the central plateau 304 (therebyincreasing the beta shielding in central portions of the lower floor302) and the outer cylindrical wall 308 of the capsule body 300. Theupper edge of outer cylindrical wall 308 forms a circular opening forreceiving outer lid 310 which is generally cylindrical but includes achambered lower circular edge 312 and further includes a centralcylindrical blind opening 314 for receiving telescoping inner lid 316,and typically forming a tight friction fit therebetween. Outer lid 310,which is typically made of titanium or stainless steel and illustratedwith an interior circumferential toroidal ridge 327, is typically weldedto capsule body 300, using conventional standards of the industry.Strontium-90 radiological insert 318 (similar to insert 130 in previousembodiments) includes an upper circular or disk-shaped portion 320 whichis engaged between a lower edge of telescoping inner lid 316 and centralplateau 304 of capsule body 300. This configuration is intended toreduce rattling of the strontium-90 radiological insert 318. The uppersurface of strontium-90 radiological insert 318 includes a convexcentral region 325. This convex central region 325 is intended toreinforce the structure and avoid or minimize warping and possibledelamination during production. Strontium-90 radiological insert 318further includes a downwardly extending circumferential toroidal portion323 which extends into toroidal channel 306 of capsule body 300.

The toroidal shape of the strontium-90 radiological insert 318, with itsthickened periphery, leads to increased radiation emission around theperiphery and a reduced radiation output within the center. This, incombination with the increased beta shielding in the central area ofcentral plateau 304, results in a flat beam profile, achieving a moreconstant absorbed dose rate throughout a target volume of tissue oftherapeutic interest that is located in front of the source) asillustrated in FIG. 5 , wherein typical values are given for aradiological source 100 of a diameter of 4.05 millimeters and a maximumheight of 1.75 millimeters. In the given example, a intended therapeuticvolume 400 with a diameter of 3.0 millimeters and a depth of 1.438 to2.196 millimeters (with a mean depth to target of 1.817 millimeters fromthe lower surface of the radiological source 100) in a first case or adepth of 1.353 to 2.111 millimeters (with a mean depth to target of1.752 millimeters from the lower surface of the radiological source 100)in a second case. A radius of 11.50 millimeters is typical for thesclera 2002 (outer covering) of a human eyeball 2000 (see also FIGS. 6and 7 ). Those skilled in the art, after review of this disclosure, willunderstand that different structural parameters will result in differentradiation distributions, as may be required by the specific application.

FIGS. 5A through 5F illustrate six further design embodiments ofradiological source 100 of the present disclosure. The radiologicalsource 100 of FIG. 5A is very similar to FIG. 3 and includes capsulebody 300 includes a lower floor 302, the interior wall of the lowerfloor 302 including a central plateau 304 on the interior thereofthereby forming a toroidal channel 306 between the central plateau 304and the outer cylindrical wall 308 of the capsule body 300. The upperedge of outer cylindrical wall 308 forms a circular opening forreceiving outer lid 310 which is generally cylindrical. Outer lid 310 istypically welded to capsule body 300, using conventional standards ofthe industry. Strontium-90 radiological insert 318 is toroidally shapedby rotating a rectangular cross-section about the central axis therebyresulting in a central passageway 319. Toroidally-shaped radiologicalinsert 318 is positioned above the toroidal channel 306, and supportedby central plateau 304 and shoulder 308A, 308B formed within an interiorof outer cylindrical wall 308. A cylindrical disk-shaped spacer 320,typically made of titanium or stainless steel, is positioned between theradiological insert 318 and the lower surface of the outer lid 310.Additionally, a cylindrical shielding insert 322, typically made fromtitanium or stainless steel, inserted within the central aperture 319.The shape of the strontium-90 radiological insert 318 leads to increasedradiation output around the periphery, with a reduced radiation outputwithin the central aperture 319. This, in combination with the increasedshielding in the central area of central plateau 304 and the cylindricalshielding insert 322, results in a flat beam profile, achieving a moreconstant absorbed dose rate throughout a target volume of tissue oftherapeutic interest that is located in front of the source (i.e.,anisotropic) characteristic of the resulting beta radiation.

The embodiment of radiological source 100 in FIG. 5B is similar to thatof FIG. 5A. The interior wall of lower floor 302 is generally planarwithout the central plateau of FIG. 5A. The toroidal-shaped strontium-90radiological insert 318 is secured to cylindrical disk-shaped spacer 320by a low-melting glass bond 321 or similar configuration. Cylindricalshielding insert 322 extends from spacer 320 to the inner wall of lowerfloor 302, thereby resulting in a configuration with a toroidal-shapedvoid 306′ below the toroidal-shaped strontium-90 radiological insert318. The shape of the strontium-90 radiological insert 318 leads to anincreased radiation source around the periphery, with a removal of asource of radiation within the central aperture 319. This, incombination with the increased shielding of the cylindrical shieldinginsert 322, results in a flat beam profile, achieving a more constantabsorbed dose rate throughout a target volume of tissue of therapeuticinterest that is located in front of the source).

The embodiment of radiological source 100 in FIG. 5C is similar to thatof FIG. 5A. The toroidal-shaped strontium-90 radiological insert 318includes a central cylindrical disk portion 318A and further includesupper and lower toroidal portions 318B, 318C, respectively, extendingaround the circumference thereof. Additionally, spacer 320 furtherincludes a downwardly extending cylindrical skirt 320A which outwardlyabuts the circumference of toroidal-shaped strontium-90 radiologicalinsert 318. Spacer 320 further includes a central cylindrical aperture320B which receives a variation of shielding insert 322, furtherincluding a downwardly extending frusto-conical portion 322A forengaging against central cylindrical disk portion 318A of strontium-90radiological insert 318 and being positioned within the upper toroidalportion 318B of strontium-90 radiological insert 318. This configurationengages the central cylindrical disk portion 318A between the downwardlyextending frusto-conical portion 322A of shielding insert 322 andcentral plateau 304. Similar to the embodiment of FIG. 5B, atoroidal-shaped void 306′ is formed between the lower toroidal portion318C of strontium-90 radiological insert 318 and the inner wall of floor302. The shape of the strontium-90 radiological insert 318 leads to anincreased radiation source around the periphery, with a reduction in theradiation from cylindrical disk portion 318A. This, in combination withthe increased shielding of the central plateau 304, results in a flatbeam profile, achieving a more constant absorbed dose rate throughout atarget volume of tissue of therapeutic interest that is located in frontof the source).

The embodiment of FIG. 5D is similar to that of FIG. 5B. However, theinterior of cylindrical wall 308 includes shoulders 308A, 308B forsupporting the toroidal-shaped strontium-90 radiological insert 318above the toroidal channel 306. This may eliminate the need for the lowmelting glass bond 321 or similar configuration to affix thetoroidal-shaped strontium-90 radiological insert 318 to the spacer 320.The shape of the strontium-90 radiological insert 318 leads to anincreased radiation source around the periphery, with a removal of asource of radiation within the central aperture 319. This, incombination with the increased shielding of the cylindrical shieldinginsert 322, results in a flat beam profile, achieving a more constantabsorbed dose rate throughout a target volume of tissue of therapeuticinterest that is located in front of the source).

The embodiment of FIG. 5E is similar to that of FIG. 5C. Thetoroidal-shaped strontium-90 radiological insert 318 includes a centralcylindrical disk portion 318A and further includes a lower toroidalportion 318C extending around the circumference thereof. The lack of aupper toroidal portion allows the spacer 320 to be simplified to acylindrical disk shape. The shape of the strontium-90 radiologicalinsert 318 leads to an increased radiation source around the periphery,with a reduction in the radiation from cylindrical disk portion 318A.This, in combination with the increased shielding of the central plateau304, results in a flat beam profile, achieving a more constant absorbeddose rate throughout a target volume of tissue of therapeutic interestthat is located in front of the source).

The embodiment of FIG. 5F is similar to that of FIG. 5E. Thestrontium-90 radiological insert 318 is simplified to a disk shape,rather than a toroidal shape. Additionally, spacer 320 further includesa downwardly extending cylindrical skirt 320A which outwardly abuts thecircumference of toroidal-shaped strontium-90 radiological insert 318.The strontium-90 radiological insert 318 is secured to cylindricaldisk-shaped spacer 320 by a low-melting glass bond 321 so as to besuspended above central plateau 304 and toroidal channel 306. It isenvisioned that this embodiment could further have the strontium-90radiological insert 318 contacting and being supported, at least inpart, by central plateau 304.

Further alternatives to the present disclosure include fixation of theactive insert using glass, such as glass pre-melted into a stainlesssteel insert, glass powder co-compacted with a ceramic and glass powdermixed with a ceramic and then compacted. Additionally, alternativesinclude fixation of the active insert using mechanical methods such assoft materials such as copper, silver, aluminum, etc. or the use ofsprings of various types (wave, conical, folded disk, etc.). Furtheralternatives include active insert centering features to preventpositional errors such as tapered ceramic disks or a disk with anaperture or protrusion which interfaces with the capsule lid.

Thus the several aforementioned objects and advantages are mosteffectively attained. Although preferred embodiments of the inventionhave been disclosed and described in detail herein, it should beunderstood that this invention is in no sense limited thereby.

What is claimed is:
 1. A radiological insert with a central portion anda peripheral portion, the central portion being relatively thinner andthe peripheral portion being relatively thicker, the central portionincluding an upwardly extending convex upper surface which extends abovethe peripheral portion and a substantially planar lower surface, whereinthe peripheral portion extends below the substantially planar lowersurface of the central portion.
 2. The radiological insert of claim 1wherein the radiological insert is toroidal shaped.
 3. The radiologicalinsert of claim 1 wherein the substantially planar lower surface, incombination with the peripheral portion, forms a substantially lowerconcave surface of the radiological insert.
 4. The radiological sourceinsert of claim 1 wherein the radiological insert includes strontium-90,wherein the strontium-90 is contained in a material or compound selectedfrom the group consisting of a strontium ceramic, a strontium glass,SrF₂, Sr₂P₂O₇, SrTiO₃, SrO, Sr₂TiO₄, SrZrO₃, SrCO₃, Sr(NbO₃)₂, SrSiO₃,3SrO.Al₂O₃, SrSO₄, SrB₆, SrS, SrBr₂, SrC₂, SrCl₂, SrI₂ and SrWO₄.